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#11830972 - 09/15/16 05:47 PM Vapor lock, boiling fuel
Biscuits Offline
Extreme Angler

Registered: 01/18/06
Posts: 2510
Loc: San Antonio
Hey guys, long time no see.
I'm running a 1984 150 Rude. I believe I'm having a vapor lock problem on hot days. The first start of the day the motor fires right up and runs great. If I sit and fish for a while the motor will usually fire right up with no problems, if I start spot hoping I start having problems. The motor gets very hard to start, if I take the cowling off and turn the valve on the choke I can hear pressure release and the motor fires right up. Then once I put it in gear the motor bogs down or dies if I give it too much fuel. It acts like its flooding out the motor. If I keep it in gear and run it just enough to move after 5 to 10 minutes it will all the sudden pick up and run great until I shut down again and then I have to repeat the process. I've read and heard these motors had vapor lock problems in the past. Is there a way to fix this?
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#11831706 - 09/16/16 07:35 AM Re: Vapor lock, boiling fuel [Re: Biscuits]
gary purdy Offline
TFF Guru

Registered: 05/24/03
Posts: 10536
Loc: Littlefield Tx & Lake A. H. US...
Have never run into this but we use to put thicker gaskets on carbs to help vapor locking. What fuel pump setup are you using?
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#11831719 - 09/16/16 07:46 AM Re: Vapor lock, boiling fuel [Re: Biscuits]
redchevy Offline
TFF Celebrity

Registered: 01/25/05
Posts: 6169
Loc: texas
How hot are your carbs/fuel lines after a run and you shut it down?

I don't think its your problem, but may try letting the motor idle a few minutes to cool off and see what happens before shutting it down.


Edited by redchevy (09/16/16 07:47 AM)

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#11831726 - 09/16/16 07:48 AM Re: Vapor lock, boiling fuel [Re: Biscuits]
Cast Online   content
TFF Team Angler

Registered: 07/31/12
Posts: 4780
Loc: North Texas - God's Country
Vapor lock is a symptom of low fuel pressure. On trucks use electric fuel pump to fix vapor lock.
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#11831800 - 09/16/16 08:32 AM Re: Vapor lock, boiling fuel [Re: Biscuits]
Biscuits Offline
Extreme Angler

Registered: 01/18/06
Posts: 2510
Loc: San Antonio
I am using a electric fuel pump, the Hopalong setup. I have tried idling a little bit before shut down and that doesn't seem to have a positive effect. It seems on hot days the problem is worse that cooler days or before noon. I'm have not thought to see if the carbs feel hot. I'll test that tonight when I'm out. I'm using the flat plugs, the UL77v. Should I try the other type of plugs? I forget the number, I thing they are 774 or something like that.
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#11831818 - 09/16/16 08:43 AM Re: Vapor lock, boiling fuel [Re: Biscuits]
redchevy Offline
TFF Celebrity

Registered: 01/25/05
Posts: 6169
Loc: texas
If its not a champion plug I would give the original part# champs a try. I have always been told only champions in OMC motors and I have personally seen a few do some weird stuff with NGK's... have also seen a few run fine with NGK's.

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#11833497 - 09/17/16 05:28 AM Re: Vapor lock, boiling fuel [Re: Biscuits]
gary purdy Offline
TFF Guru

Registered: 05/24/03
Posts: 10536
Loc: Littlefield Tx & Lake A. H. US...
I don`t know where your pump is located but I have less problems when I mount the electric pumps away from the outboard motor and closer to the fuel tank.
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“The world will not be destroyed by those who do evil, but by those who watch them without doing anything” GOD IS GOOD

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#11833515 - 09/17/16 05:59 AM Re: Vapor lock, boiling fuel [Re: Biscuits]
Biscuits Offline
Extreme Angler

Registered: 01/18/06
Posts: 2510
Loc: San Antonio
My fuel pump is port side right next to the motor. Are you suggesting moving it outside the motor next to the fuel bulb? What is weird is the motor has run great all summer, this has been a recent development, like within the last month. I bought new plugs last night (77JC4). As soon as it gets light enough I'm going to install them and give it a try this morning.

One thing I noticed the other day was I pulled my plugs and it looks to me that number 3 plug is cleaner than the rest of the plugs. I checked the spark with my tester and it looks like I am getting spark to that plug. It was hard to tell in the daylight but I'm wondering if that coil is getting weak. Could that also be a source of my problem? When the coil is hot it is not working right?
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#11833746 - 09/17/16 09:36 AM Re: Vapor lock, boiling fuel [Re: Biscuits]
Dubee Offline
Extreme Angler

Registered: 07/17/11
Posts: 1199
Loc: Godley Tx
Put a cool can on it. Lol

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#11834228 - 09/17/16 05:20 PM Re: Vapor lock, boiling fuel [Re: Biscuits]
Biscuits Offline
Extreme Angler

Registered: 01/18/06
Posts: 2510
Loc: San Antonio
I put in the new plugs this morning and believe it or not the problem seems to be worse. There really is no one thing that I can pinpoint that is causing the lose of power. About half the time if I turn the choke knob and let the motor run for about 30 seconds then maybe once I put the cowling back on I can run at WOT but as soon as I shut down I'm dealing with the problem again.
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#11834602 - 09/17/16 08:28 PM Re: Vapor lock, boiling fuel [Re: Biscuits]
SteezMacQueen Online   happy
TFF Team Angler

Registered: 11/02/14
Posts: 3049
Loc: Red Oak, Galveston, and Pagosa...
By chance did you start buying fuel at a difference gas station? Did the gas station meet its requirements for volume of the name brand (if it IS a name brand fuel) and now they can buy cheap fuel from someone else?

Carbs don't just start to vapor lock. It is usually an issue with fuel quality, carbon build up (likely), and/or timing could be off a tiny bit causing the motor to run a little hotter.

I don't know. I'm not an outboard mechanic by any stretch. But these are symptoms that I have encountered with older, non-fuel-injected motors.
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#11834640 - 09/17/16 08:43 PM Re: Vapor lock, boiling fuel [Re: Biscuits]
Biscuits Offline
Extreme Angler

Registered: 01/18/06
Posts: 2510
Loc: San Antonio
I'm buying my fuel at Walmart and Valero so I pretty sure it is good. Its funny you mention timing because I'm starting to think the timing has some how got thrown off. I have not touched the link and sink but I am wondering if that is the problem.

Ok here is a new development. I was out on the lake tonight and the same thing happened with feeling like the motor is running rich. I took the cowling off and the motor ran great. What does that tell you?
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#11835060 - 09/18/16 06:14 AM Re: Vapor lock, boiling fuel [Re: Biscuits]
gary purdy Offline
TFF Guru

Registered: 05/24/03
Posts: 10536
Loc: Littlefield Tx & Lake A. H. US...
Ignition wire shorting out.
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“The world will not be destroyed by those who do evil, but by those who watch them without doing anything” GOD IS GOOD

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#11836773 - 09/19/16 09:17 AM Re: Vapor lock, boiling fuel [Re: Biscuits]
Biscuits Offline
Extreme Angler

Registered: 01/18/06
Posts: 2510
Loc: San Antonio
I seemed have missed place my book with the wiring diagram. Can you tell me the color of the ignition wire.
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#11838846 - 09/20/16 09:06 AM Re: Vapor lock, boiling fuel [Re: Biscuits]
Biscuits Offline
Extreme Angler

Registered: 01/18/06
Posts: 2510
Loc: San Antonio
The wire seems to fine. I see no corrosion. I pulled my carbs and all are clean. I did the link and sink and checked all the timing. Still the same problem. Number three plug looks like it is running a little lean. The motor is running great on the first start of the day but after that it is very boggy and dies if I give it 1/4 throttle.
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